The present invention relates to a method of improving the thermal properties of polyphenylene ether, by blending the polyphenylene ether with a siloxane fluid having a critical mole % of chemically combined phenylsiloxane units. More particularly, the polyphenylene etherphenylsiloxane fluid blends provided by the method of the present invention, have been found to possess a reduction in both peak smoke release rate and total smoke when tested in accordance with ASTM E906-83.
Prior to the present invention, as shown by Haaf, U.S. Pat. No. 3,737,479, thermoplastic compositions are provided of polyorganosiloxane and polyphenylene ether having improved drop-weight impact resistance. Lovgren et al, U.S. Pat. Nos. 4,446,090 and 4,487,858, show that high viscosity silicone fluids have been blended with thermoplastic polymers to produce flame retardant thermoplastic materials.
In copending application Ser. No. 07/455,122, filed Dec. 22, 1989, there is described thermoplastic flame retardant silicone-polyphenylene ether graft copolymers resulting from the oxidative coupling of certain phenylsiloxane macromers and 2,6-diorganophenol. It was found that in addition to being a flame retardant high performance thermoplastic, the silicone-polyphenylene ether graft copolymer also produced about a 30% by weight of intumescent residue upon termination of burning. The residue remaining after combustion is sometimes referred to as "char yield". Char yield can be measured by the burning of a 1/2" '3/4".times.1/16th" molded sample of polymer after it has been placed 2 inches from a radiant heat panel having a 4.4 watts/cm.sup.2 heat flux. A desirable char is a char which intumesces or swells, since the char can provide an insulating layer between the heat of the flame and the substrate and behave as a mechanical shield to reduce smoke evolution.